Hazy Days

If you live on the East Coast, there's a good chance you've hated the weather this last week. Day after day, a cloudy haze of oppressively hot, humid, stagnant air hung over the region.

The main culprit for these conditions is high atmospheric pressure, which maintains a stable, stagnant block of air. This causes human pollution - emissions from vehicles, power plants, and forest fires - to get stuck in the air, making the situation even worse.

When conditions are hot and uncomfortable, more people crank up their refrigeration and air conditioning devices, creating a larger demand for electricity. This makes the power plants work more and emit more pollution. It's a vicious cycle.

All week the Environmental Protection Agency issued air quality warnings as pollution levels reach the "Unhealthy for Sensitive Groups" category in many areas. In these conditions, people with respiratory problems are advised to stay indoors and even healthy people are cautioned against too much outdoor activity.

Fortunately, weather forecasters are predicting that the high pressure will break towards the end of the week, as cool, clean air sweeps in from Canada.

This image was taken July 26 by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite.

--Bjorn Carey

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Credit: NASA Earth Observatory